Bui. 1136, U. S. Dept. of Agriculture. 
PLATE VI 
Thermostatic Air Valves and Traps. 
In those illustrated the thermostatic element consists of a flexible capsule C and 
a volatile or nonvolatile liquid, the expansion of which shuts the valve. The 
capsules serve as springs to open the valves. The traps are provided with ad- 
justing nuts A to compensate for variations in the steam pressure in the system. 
